1. Field of the Invention
The present invention relates to a one-way clutch used as a part for performing transmission of torque, back stop and the like in a driving apparatus for an automobile, and more particularly, it relates to a holder or retainer for holding torque transmitting elements used in such one-way clutch.
2. Related Background Art
In general, a one-way clutch includes a plurality of torque transmitting elements arranged between an inner ring or race and an outer ring or race, and is so constructed that, only when the inner ring or outer ring is rotated in one direction, torque is transmitted to the outer ring or inner ring, and when the ring is rotated in the other direction the torque is not transmitted. Sprags or rollers are used as the torque transmitting elements, and the rotational force is transmitted or not transmitted through engagement or disengagement between the torque transmitting elements and the rings.
The sprag-type one-way clutch is, for example, as shown in FIGS. 13 to 15, constituted by an annular inner ring 50 having an outer peripheral surface 52, an annular outer ring 54 arranged coaxially with the inner ring and having an inner peripheral surface 56 opposed to the outer peripheral surface 52, a plurality of sprags 58 arranged in and along an annular space defined between the outer and inner rings at regular intervals in the circumferential direction, and inner and outer holders 60, 62 for holding the sprags in predetermined positions and driving the sprags simultaneously. The sprags 58 are biased by means of a ribbon-shaped spring 68.
The inner holder 60 and outer holder 62 are used for holding or maintaining each of the sprags 58 in the predetermined respective position and for synchronizing the movements of the sprags 58. To this end, the holders 60 and 62 positioned in the annular space between the inner and outer rings must always be kept or maintained in respective given or fixed radial positions. In order to keep each of the holders in the respective given position, the holders are provided at one of their axial ends with flanges 64 and 66, respectively, which are opposed to the outer peripheral surface 52 of the inner ring 50 and the inner peripheral surface 56 of the outer ring 54, respectively, whereby the holders 60 and 62 are guided by the inner ring 50 and outer ring 54, respectively. In this way, the holders 60 and 62 can be rotated in the circumferential direction relatively while keeping their given radial positions, as inner and outer rings 50 and 54 are rotated, thus synchronizing the movements of the sprags 58.
Ideally, the flanges should be formed on both axial ends of each of the holders 60, 62 to guide these. However, it is difficult to manufacture such holder having flanges on its both ends, and thus, the clutch will be expensive. For this reason, in general, the holder having a flange formed on one end has still been widely used in the one-way clutch. However, when the holder having a flange on one end is used in the one-way clutch, there is a risk that a center of the holder will become offset from the centers of the inner ring 50 and the outer ring 54 (i.e., a so-called "bounding phenomenon"), as shown in FIG. 15 in the case of holder 60. If such bounding phenomenon occurs, the sprags and the like will be subjected to abnormal or premature wear, resulting in failure of the one-way clutch.
In addition, when the inner ring 50 or the outer ring 54 is suddenly accelerated or decelerated during rotation, the sprags 58 are slid between the inner peripheral surface 52 and the outer peripheral surface 56 due to inertia, thus wearing down the sprags. In order to prevent such sliding movement of the sprags, a squeezing or dragging torque may be applied between the inner ring 50 or outer ring 54 and the holders 60, 62 to rotate the ring 50 or 54 together with the holders 60 and 62, thereby synchronizing the movement of the sprags 58 with that of the inner ring 50 or outer ring 54. In this case, however, since drag pieces 70 such as drag clips and drag strips must be provided, the number of parts for the clutch is increased and the assembling operation is complicated, thus increasing the cost of manufacture of the clutch. In order to apply the dragging torque, in some cases, in place of the drag pieces, notches have been formed on the holders 60 and 62 to provide I bars or T bars; however, also in this case, there remained the problems in workability and stability of the holders.
As stated above, in the conventional one-way clutch of this kind, it has been economically impractical to keep the holders in the given position by forming the flanges on both axial ends of each holder. Nor has it been feasible as a practical matter to apply the dragging torque to keep the holder in the given position without increasing the number of parts.